The term "polyphenylene ether resin" includes a family of polymers well known to those skilled in the art. They are made by a variety of catalytic and non-catalytic processes from the corresponding phenols or reactive derivatives thereof. By way of illustration, certain of the following polyphenylene ethers ae discussed in Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875, and in Stamatoff, U.S. Pat. Nos. 3,257,357 and 3,257,358. Also, the Bennett and Cooper patents, U.S. Pat. Nos. 3,639,656, 3,642,699, 3,661,848 and 3,730,944 (Bennett and Katchman) describe processes for the preparation of polyphenylene ethers. In the Hay patents, the polyphenylene ethers are prepared by a oxidative coupling reaction comprising passing an oxygen-containing gas through a reaction solution of a phenol and a metal-amine complex catalyst. Other disclosures relating to processes using metal-amine catalysts are found in Bussink et al, U.S. Pat. No. 3,337,499; Blanchard et al, U.S. Pat. No. 3,219,626; Laakso et al, U.S. Pat. No. 3,342,892; Borman, U.S. Pat. No. 3,344,166; Hori et al., U.S. Pat. No. 3,384,619; Faurote et al., U.S. Pat. No. 3,440,217; and disclosures relating to metal based catalysts which do not include amines, are well known from patents such as Wieden et al, U.S. Pat. No. 3,442,885 (copper-amidines); Nakashio et al., U.S. Pat. No. 3,573,257 (metal-alcoholate or phenolate); Kobayashi et al., U.S. Pat. No. 3,455,880 (cobalt chelates); and the like. In the Stamatoff patents, the polyphenylene ethers are produced by reacting the corresponding phenolate ion with an initiator, such as a peroxy acid salt, an acid peroxide, a hypohalite, and the like, in the presence of a complexing agent. Disclosures relating to non-catalytic processes, such as oxidation with lead dioxide, silver oxide, etc., are described in Price et al., U.S. Pat. No. 3,382,212. All of the patents which are mentioned above are incorporated herein by reference.
The Cizek patent, U.S. Pat. No. 3,383,435 discloses compositions of polyphenylene ether resins and styrene resins. The thermoplastic compositions disclosed by Cizek may include a rubber-modified styrene resin, as well as crystal polystyrene. This patent is hereby incorporated by reference.
In the prior art certain compositions of polyphenylene ethers and polyorganosiloxanes have been described. For example, U.S. Pat. No. 3,737,479 discloses the use of certain types of organosiloxanes as impact modifiers for polyphenylene ether resin compositions. Also, U.S. Pat. No. 3,063,872 discloses certain types of organopolysiloxanes in combination with polyphenylene ethers. Those compositions are mentioned as having special utility in recording, storing and reproducing photographic images. All of the compositions disclosed in these prior art patents were limited to organosubstituted polysiloxanes and did not teach compositions of a polyphenylene ether with organopolysiloxanes having Si--H bonds.
Polyphenylene ether resin compositions that include alkenyl aromatic resins such as styrene resin, exhibit a propensity for discoloration when they are extruded and molded. This discoloration is manifested as a yellowish tinge that is particularly objectionable when white or pastel-colored products are being manufactured. Therefore, thermally stable polyphenylene ether-alkenyl aromatic resin blends are particularly useful.
It has now been found that the use of a minor amount of an organopolysiloxane, having Si--H bonds, as an additive to thermoplastic polyphenylene ether-alkenyl aromatic resin compositions will contribute to the thermal stability thereof.
Accordingly, it is a primary object of this invention to provide thermoplastic compositions which comprise a polyphenylene ether and an alkenyl aromatic resin, which do not exhibit thermal discoloration when they are processed through an extrusion and molding cycle.
It is also an object of this invention to provide thermoplastic compositions which comprise polyphenylene ethers and an alkenyl aromatic resin which exhibit improved thermal stability without substantially affecting the tensile strength, elongation, impact strength or heat distortion temperature.